He's a beauty, and a really nice boy, but he's stressed. The divided 10 gallon is putting a lot of strain on him. I think he'd do better by himself. I've considered swapping tanks with one of my other guys, but Draco hasn't been doing so well either, and I'm afraid of the same thing will happen to both the moved fish and Draco. So, my idea was to find Thor a caring, responsible home and give Draco the entire 10 gallon to himself.

Had a bad experience with a divided tank myself.
My favorite and first DTHM boy got really stressed out and started tail bitting. I added another 2 layers of the craft mesh so they could not see eachother. But it didn't work. I think he felt the other fish and just that stressed him out enought.
I changed him back to a tank by himself but the damage was already done and he died a short time after that.
I regretted the divided tank so much and only keep separate tanks now.
Hopefully your little guy will be stronger than mine and go back to his old self soon.
Good luck!

I think I would have to if someone was willing to take him. I still haven't decided yet, though.

I haven't had much success with homemade dividers--I originally divided the tank in three with the storebought divider and a homemade one, and thank goodness I didn't put them right next to each other, because Draco pushed through. I'm not sure what I'm doing wrong there, because I know other people have used homemade ones just fine.

Yeah a critter keeper is a great idea. I have lots of homemade dividers and don't have problems. It did take a bit to get the hang of placing them right so the fish couldn't get through though. It may also just be his personality. I have one who has to be alone or bites his tail. I assume he's just biting his tail right? Not damage from another betta getting through a divider?